Plant diseases are often a serious limitation on agricultural productivity and therefore have influenced the history and development of agricultural practices. A variety of pathogens are responsible for plant diseases, including fungi, bacteria, viruses, and nematodes. Among the causal agents of infectious diseases of crop plants, however, fungi are the most economically important group of plant pathogens and are responsible for huge annual losses of marketable food, fiber, and feed.
Incidence of plant diseases has traditionally been controlled by agronomic practices that include crop rotation, the use of agrochemicals, and conventional breeding techniques. The use of chemicals to control plant pathogens, however, increases costs to farmers and causes harmful effects on the ecosystem. Consumers and government regulators alike are becoming increasingly concerned with the environmental hazards associated with the production and use of synthetic agrochemicals for protecting plants from pathogens. Because of such concerns, regulators have banned or limited the use of some of the more hazardous chemicals. The incidence of fungal diseases has been controlled to some extent by breeding resistant crops. Traditional breeding methods, however, are time-consuming and require continuous effort to maintain disease resistance as pathogens evolve. See, for example, Grover and Gowthaman (2003) Curr. Sci. 84:330-340. Thus, there is a substantial interest in developing novel alternatives for the control of plant pathogens that possess a lower risk of pollution and environmental hazards than is characteristic of traditional agrochemical-based methods and that are less cumbersome than conventional breeding techniques.
Recently, agricultural scientists have developed crop plants with enhanced pathogen resistance by genetically engineering plants to express antipathogenic proteins. A continuing effort to identify antipathogenic agents and to genetically engineer disease-resistant plants is underway.
Thus, in light of the significant impact of plant pathogens, particularly fungal pathogens, on the yield and quality of crops, new compositions and methods for protecting plants from pathogens are needed.